The Study Of Position Control Characterstics Of Cell Hydraulic Lifter

The most prominent advantages of electro-hydraulic servo system are fast response, high output power and precision control. As a result, electro-hydraulic servo system is widely used in various fields.According to the advantages of electro-hydraulic servo system, it is applied to control the laboratory lifter which is used to electrolytic aluminum reaction. In this paper, the structure and control system's characteristics of the lifter are analyzed comprehensively.Based on the analysis results, the characteristics which are not meet the stability performance requirements are corrected, in order to improve the overall performance of system.The main research in this paper as following:First of all, the lifter is detailed designed from three aspects-machinery, electricity and hydraumatic, respectively. In order to meet the requirements of electrolytic aluminum reaction conditions, the mechanical structure of lifter is a three-beam and four-post. The electrical control system not only guarantees the lifter can complete the action of up and down, but also uses the displacement sensor to constitute the closed-loop feedback of control system, to adjust the position of moving beam accurately. Hydraulic system is the power source of the lifter, to ensure the smooth functioning of the system.Second, the mathematical model is established of the system which contains asymmetric cylinder controlled by symmetrical valve. Because of the asymmetric cylinder, the mathematical model is theoretical analyzed specifically for different forms of exercise. After linearization the associated equation, the different motion mathematical models of the system are derived. A unified mathematical model is obtained by analyzing the different forms in depth. In theory, the mathematical model is well prepared for the analysis of system characteristic.Again, the characteristic of the system is analyzed by using MATLAB. Through theoretical analysis, the parameters'range which ensures system stability is determined. By using Simulink, the parameters' value range is confirmed to be correct. The closed-loop transfer function is obtained, and the stiffness characteristics and the response characteristic of the closed-loop system are simulated and analyzed. Because the precision requirement of the lifter is strict, the steady-state error of the system is analyzed. The result does not meet the requirement, so the system needs correction.Finally, the system is respectively calibrated by lag correction and PID controller. Depending on the system accuracy and stability requirements, the lag correction improves the system accuracy. Although the accuracy is ensured, both the closed-loop system bandwidth and the system response speed is reduced. PID controller is equivalent to lead-lag correction network. It not only improves system accuracy, but also increases the effective bandwidth of the closed-loop system and some other performance. Comparing the two correction methods, PID controller is used to calibrate the system.